01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together gluten-free flour blend, baking powder, and salt. Set aside.
03 - In a large bowl, beat together unsalted butter and granulated sugar using an electric mixer or hand whisk until light and fluffy, about 2 minutes.
04 - Mix in the egg, lemon zest, lemon juice, and vanilla extract until fully combined.
05 - Gradually add dry ingredients to wet mixture, mixing until just incorporated without overbeating.
06 - Gently fold in chopped pistachios to evenly distribute.
07 - Scoop tablespoon-sized portions of dough, roll into balls, and coat each lightly in extra granulated sugar.
08 - Place dough balls 2 inches apart on prepared baking sheets. Flatten gently using your palm or the bottom of a glass.
09 - Bake for 10 to 12 minutes, until the edges are lightly golden.
10 - Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.